Laser-induced breakdown spectroscopy (LIBS) is a novel technology for analyzing physical elements which is developed in the late 20th century. The operating principle of LIBS is that: under the effect of a strong laser pulse, within a region of the surface of a sample on which the laser focuses, atoms, molecules and the like, which constitute the sample substance, are actuated into plasma after a series of processes including multiphoton ionization, absorption of photons, acceleration, impact etc.; and the actuated plasma decays rapidly after the strong laser pulse is stopped, during which photons with specific frequencies are radiated thereby generating characteristic spectral lines, and information of types and concentrations of elements of the object being analyzed are included in the information about frequencies and intensities of the photons. The LIBS technology has the advantages of low operating cost, fast measurement speed, high sensitivity, multi-element measurement without or with very simple pretreatment of the sample and with no radiation hazard, and thus it has great potential for development in industrial production.
However, in LIBS, as the point where laser focuses is very small, the amount of the ablated substance is very little, thus the matrix effect is significant to an inhomogeneous, anisotropic substance. Meanwhile, the variability of laser energy and the differences of physical parameter, such as the temperature of plasma, the density of electrons and the like, cause the low repeatability of the LIBS measurement. Moreover, both the influence of environmental parameters and the electrical noise from the components of the instrument per se tend to interference the LIBS. Thus, there is no guarantee to the accuracy of measuring the sample directly by the LIBS, which restricts the application of the LIBS in actual production.
In order to resolve the above problems, in the prior measurement technology, a sample is typically simply preprocessed to improve the accuracy of element measurement, for example, the sample powder is pressed to improve the reproducibility of the LIBS measurement, the sample is grinded, mixed uniformly to weaken the matrix effect etc. But the uncertainty of measurement or various influences still can not be eliminated completely and direct measurement may not achieve the accuracy required by industrial production, thus a further research for the preprocess method of sample is still needed.